Fuse structure



W. D. KYLE FUSE STRUCTURE Dec. 11, 1934.

Filed Oct. 24, 1929 dttoamq Patented Dec. 11, 1934 UNITED STATES PATENT OFFICE Application October 24, 1929, Serial No. 402,041

3 Claims.

This invention relates to fuse structures, and is particularly directed to a fuse structure which is applicable to relatively high voltage circuits.

In the manufacture of fuses of the above identified type, it has been found that when the fuse cartridge is formed of fiber, that it will stand a considerable amount of heat, but, as compared with other insulators, it is a poorer dielectric and takes up some degree of moisture. To overcome this difficulty, it has been the practice to form these fuse cartridges with an insulating outer shell of phenol condensate and a fiber inner tube. The phenol condensate, although it carbonizes more readily than fiber, has a very much higher dielectric characteristic and. also does not take up moisture.

Heretofore it has been the practice to provide two complete tubes, the inner tube of fiber and the outer tube of phenol condensate, such tubes extending from the upper contact member to the lower contact member. This construction, however, is expensive and employs a considerable amount of insulating material, such, for instance, as the relatively expensive phenol condensate, at a portion of the structure where it is not required.

It has been found, through extensive experimentation, that the difference of potential that exists between the outer side of the cartridge and its inner portion, both at the time when the fuse blows or melts and after the blowing of the fuse, is greatest adjacent that end of the fuse cartridge which is merely surrounded by the metallic contact member, and that the other end of the cartridge in which the metallic member extends to the interior of the tube or crosses the upper open end, does not have this high difference of potential between the inner and outer sides of the tube structure.

From actual tests conducted with fuse cartridges which consisted of a tube whose upper end is closed by a metallic contact member and whose lower portion is merely surrounded by a metallic member, it has been found that frequently the insulating tube punctures, carbonizes or is otherwise injured adjacent the lower end which is merely surrounded by the metallic, conducting contact member. This result is found to. be substantially uniform in a long series of tests.

While the theory underlying this action may not be fully understood, it is believed that due to the fact that the upper contact member actually spans the upper end of the tube, that it may be considered as in communication with the interior of the tube, it being considered, of course, that the arc or any ionized gases within the tube cartridge constitutes a conductor. Consequently, there is, at most, only a relatively very slight difference of potential 5 between the metallic contact member and the interior of the fuse tube. At the lower end of the fuse tube, however, where the metallic, conducting contact member merely surrounds the tube, it is clear that there is a very high difference of potential between the interior of the tube and the exterior surrounding contact member. Presumably rupturing of the tube at this lower portion is due to the above described relatively high difference of potential.

Even if rupturing at the lower portion does not occur, there is still a chance of leakage unless a very high dielectric is interposed between the metallic lower contact member and the inner or main tube. In addition to this, there is a tendency for leakage to occur from the lower contact member, either along the outer surface of the tube or through the tube, so that radio disturbance is very frequently set up.

This invention is designed to overcome the defects noted above, and objects of such invention are to provide a fuse structure in which a relatively cheap inner tube may be provided which constitutes the main body of the cartridge, and in which a high dielectric outer sheath or tube is provided for the lower end of the main tube, such outer dielectric sheath being interposed between the lower contact member and the main tube, thereby protecting the structure against puncturing, carbonizing or leakage, While at the same time materially reducing the cost of construction.

Further objects are to provide a novel construction for a relatively high voltage fuse structure in which the high dielectric insulating outer tube is held in place in a manner which avoids any possible lessening of the dielectric characteristics of the structure and which, at the same time, provides a structure which is very easy to produce and assemble.

Further objects are to provide a fuse structure which is a commercial and practical article of manufacture, which withstands severe use, and which has a long, effective life.

Embodiments of the invention are shown in the accompanying drawing, in which:-

Figure l is a fragmentary, sectional elevation of a fuse box with one form of the novel fuse structure shown in place and partly in section.

Figure 2 is a sectional view on the line 2-2 of Figure 1.

Figure 3 is a fragmentary view of the lower portion of the cartridge or tubular structure of a modified form of the invention, such view being partly in section.

Figure 4 is a sectional View drawn on the line 4-4 of Figure 3, drawn to an enlarged scale.

Figure 5 is a view corresponding to Figure 3, showing a further form of the invention.

Figure 6 is a view corresponding to Figure 3, showing a still further form of the invention.

It is to be distinctly understood, before entering the detailed description of this invention, that the fuse structure may take a great many other forms than those shown, and that the forms shown are merely some of the many practical constructions that may be employed. It is also to be understood that although, for the sake of clearness, one of the contact members will be referred to as the upper contact memher and the other as the lower contact member, nevertheless these expressions upper and lower are merely used to identify the parts, and the invention is not to be limited by a strict application of these terms, as, obviously, the fuse structure could occupy other positions from that shown in the drawing without in the least Way departing from the spirit of this invention.

Referring to Figures 1 and 2, it will be seen that a portion of a fuse box has been shown, the back being indicated at 1 and the door or front at 2. The back 1 of the fuse box normally carries an upper contact receiving clip 3 and a lower contact receiving clip 4. The door 2 may be slotted so that the projecting portion 5 of the fuse carrier or mounting 6 may project therefrom. This fuse carrier or mounting is preferably formed of phenol condensate and may be locked to the fuse box door 2 in any suitable manner, as by means of the winged thumb piece '7. This particular form of construction, however, maybe varied. It is merely given as an illustration of one of the possible constructions with which the fuse structure may be used. The fuse carrier 6, or mounting, is provided with a pair of arms 8 which project beyond the body portion of the carrier 6 and which receive between them the main tube 9 of the fuse. The

-fuse tube or main tube 9 may be locked to the carrier in any suitable way, for instance, by means of the cross-strap 10 held in place by screws, as shown in Figures 1 and 2. The carrier 6 is preferably slightly recessed to accom- -modate the fuse cartridge.

The main tube 9 carries a metallic upper contact member 11 which is secured thereto in any suitable manner, for instance, by threading and screwing the tube 9 into the metallic contact member 11. This metallic contact member 11 extends across the upper otherwise open end of the main tube 9 and is provided with a fuse clamping metal cap 12. In other words, the upper contact member has a metallic portion which is in communication with the interior of the cartridge.

Fiber has been found highly suitable for the main tube 9 which forms the body portion of the fuse structure, but obviously other materials could be used. The fiber, however, is subject to certain defects, for example, it is not as good a dielectric as phenol condensate and takes up moisture to a certain extent. It is, however, satisfactory in this construction, for the defects 7 are cared for in another manner and as the fiber has the highly desirable characteristic of withstanding a relatively high degree of heat without carbonization.

The lower portion of the main fiber tube 9 is surrounded by an outer tube or sheath 13 which is preferably formed of phenol condensate. At all events, it is formed of an insulating material Which has a very high dielectric strength and which does not take up moisture. This outer tube or sheath 13 extends over a considerable portion of the lower part of the tube 9, but it does not extend to a very great distance upwardly along the tube 9.

At this point it is to be noted that various means may be employed for holding the outer high dielectric sheath in place. For example, as shown in Figure l, the tube carrier or mounting 6 may be provided with a notched-out portion which receives a projection or flange 14 carried by the outer sheath or tube 13 and preferably formed integrally therewith. This construction, outlined immediately above, prevents shifting of the sheath or tube 13 upon the main tube 9.

The high dielectric sheath or tube 13 carries ...-1

the lower contact member 15 which may be locked thereto in any suitable manner, as, for example, by means of a small screw 16. The lower contact member 15 is adapted to be received by the contact receiving clip 4. This lower contact member 15 has a downwardly extending tubular portion which is provided with a threaded part 1'7 and with a tapered portion 18. It stops short of the lower and of the upper end of the phenol condensate outer tube or sheath 13, as shown in Figure 1, and preferably the threaded portion 17 is provided with a notch 19 in which the lower end of the fuse strip 20 may be positioned. A threaded metal nut 21 is screwed upon the threaded portion 17 of the lower contact member and is provided with a tapered portion cooperating with the tapered portion 18 to clamp the fuse in place.

It is to be distinctly understood that although an expulsion type of fuse has been illustrated and a specific type of fastening for the fuse strip shown, nevertheless the invention is applicable to other types of fuse structures, and also that other types of fuse attaching means may be employed.

From the description thus far given, it will be seen that the fuse structure employs the main tube 9, preferably formed of fiber, which is kept by the metallic upper contact member, and that a high dielectric insulating sheath surrounds the fiber tube and is held in place thereon and carries the lower contact member. The lower contact member, it is to be noted particularly, does not communicate with the interior of the tube.

When the fuse blows, the fiber main tube 9, which extends throughout the entire length of the tubular structure, withstands the high heat. Also, it will be seen that after the fuse strip has been destroyed or expelled, that there is no communication between the lower contact member 15 and the interior of the tube. Consequently there is, at this point, a relatively high potential difference. This relatively high potential difference is taken care of by means of the sheath 13 which, as stated, has very high dielectric characteristics and is moisture-proof as well. Consequently, there is no chance of rupturing the cartridge or tube at any point, for, at the point where the greatest strain occurs, the maximum insulation is provided. In addition to this,

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it is to be noted that no leakage can occur, as the phenol condensate outer sheath 13 is moisture-proof and is not subjected to any intense heat. Therefore, there is no possible chance of even a small leakoccurring at this point or, in fact, at any point along the tube cartridge. Small leaks occurring in fuses produce radio disturbances and also produce a slow carbonization of the fuse cartridge. It is, therefore, clear that this invention guards against one of the frequent sources of trouble of this general type.

The invention may take other forms. For example, as shown in Figures 3 and 4, the fiber tube or main tube 22, corresponding to the tube 9 of Figure 1, has its lower portion covered by a phenol condensate tube or sheath 23 which is held in place by means of a pin 24 of insulating material, such, for instance, as fiber or phenol condensate, which is passed through openings in the lower tube or outer tube 23 and through a groove or key-way formed in the outer surface of the inner tube or main tube 22, as shown in Figure 4.

A further form is shown in Figure 5, in which the main fiber tube 25 is slightly tapered at its lower end, A phenol condensate outer sheath or tube 26 is slipped over this tapered end and is correspondingly internally tapered. A drive fit is obtained between these members.

A still further form of the invention is shown in Figure 6 in which the fiber tube or main tube 27 is provided with a roughened lower portion 28 upon which an outer phenol condensate tube 29 is formed as by molding, for instance. The phenol condensate tube, therefore, secures a very firm grip upon the lower end of the fiber tube.

It is apparent that the invention may take still other forms although several specific embodiments have been illustrated.

It will be seen that a novel form of fuse structure has been provided by this invention which is relatively simple, which has high dielectric characteristics, which is economical to make, and which has a long, effective life.

It is to be noted particularly that when the fuse blows, the ionized air within the tubular fuse cartridge forms a conducting medium. The upper contact member is in communication with the interior of the tubular cartridge and consequently there is no material potential difference between the interior of the cartridge and the upper contact member. However, there is a sharp or steep potential gradient between the interior of the tubular cartridge and the lower contact member which surrounds the cartridge but is out of communication with the interior thereof. It is to be noted particularly that this invention provides a thickened lower portion for the tubular cartridge to provide for this steep potential gradient occurring at this portion of the structure. There is, therefore, no chance of rupturing the tubular cartridge.

It is to be distinctly understood that the expressions upper and lower or similar expressions used in defining the contact members or adjacent portions of the tubular or cartridge structure, are used in the claims only for the purpose of clearness and not for the purpose of specifically limiting the claims to members located at these relative positions. Obviously, the fuse structure would preferably be used in a vertical position, but it might be used in other positions, and consequently it is not intended that these terms shall be construed as specifically limiting the structure, but are to be understood merely as a convenient way of identifying the two ends of the main tube and the correspondingly located contact members.

Although this invention has been described in considerable detail, it is to be understood that such description is intended as illustrative rather than limiting, as the invention may be variously embodied and is to be interpreted as claimed.

I claim:

1. A fuse structure comprising a main fiber tube having open ends, an upper contact member secured to said tube and extending across the upper end of said tube and communicating with the interior of said tube, a phenol condensate sheath molded around the lower portion of said fiber tube and extending partway only along said fiber tube, a lower contact member surrounding said phenol condensate sheath, said lower contact member being out of communication with the interior of said tube, and a fuse element positioned Within said fiber tube and normally connecting the upper and lower contact members.

2. A fuse structure comprising a main fiber tube having open ends, an upper contact member carried by the upper end of said tube, the exterior lower portion of said fiber tube being roughened, a phenol condensate sheath molded around the roughened portion of said fiber tube, a lower contact member secured to said phenol condensate sheath, and a fuse element extending through said fiber tube and normally connecting the upper and lower contact members.

3. A fuse structure comprising a fiber tube, an upper contact communicating with the interior of the tube, a phenol condensate sheath molded around the outer portion of said fiber tube adjacent its lower end and bonded to said fiber tube, a lower contact out of communication with the interior of said fiber tube and surrounding said phenol condensate sheath, and a fuse link normally extending from said up per contact, through said fiber tube to said lower contact, whereby when said fuse blows, the resulting steep potential gradient between the interior of the fiber tube and the surrounding lower contact is provided for by the extra insulation afforded by the phenol condensate sheath and the fiber tube which form a bonded structure.

WILLIAM D. KYLE. 

